Abstract
The significant heat loss and severe thermal fluctuations inherent in steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS) impose considerable constraints on well cementing. In order to obtain better energy efficiency and mechanical robustness, there is considerable interest in the development of low-thermal-conductivity cement that can provide a combination of enhanced thermal insulation and mechanical resilience upon thermal cycling. However, the current palette of thermal cements is exceedingly sparse. In this article, we illustrate a method for decreasing the thermal conductivity of cement by inclusion of hydroxyethylcellulose-functionalized halloysite nanotubes. Halloysite/hydroxyethylcellulose inclusions offer an abundance of disparate interfaces and void space that can effectively scatter phonons, thereby bringing about a pronounced reduction of thermal conductivity. The microstructure of the nanocomposite cementitious matrix is strongly modified even as the compositional profile remains essentially unaltered. Modified cement nanocomposites incorporating halloysite nanotubes along with hydroxyethylcellulose in a 8:1 ratio with an overall loading of 2 wt.% exhibit the lowest measured thermal conductivity of 0.212 ± 0.003 W/m.K, which is substantially reduced from the thermal conductivity of unmodified cement (1.252 W/m.K). The ability to substantially decrease thermal conductivity without deleterious modification of mechanical properties through alteration of microstructure, inclusion of encapsulated void spaces, and introduction of multiple phonon-scattering interfaces suggests an entirely new approach to oilwell cementing based on the design of tailored nanocomposites.
Highlights
The significant heat loss and severe thermal fluctuations inherent in steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS) impose considerable constraints on well cementing
We report a pronounced reduction in the thermal conductivity of oilwell cement upon inclusion of polymer-functionalized halloysite nanotubes (HNTs)
The available palette of thermal cements is rather sparse despite the urgent need for low-thermal-conductivity cement for applications such as SAGD wherein heat loss to the external environment represents a considerable expense
Summary
The significant heat loss and severe thermal fluctuations inherent in steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS) impose considerable constraints on well cementing. The ability to substantially decrease thermal conductivity without deleterious modification of mechanical properties through alteration of microstructure, inclusion of encapsulated void spaces, and introduction of multiple phonon-scattering interfaces suggests an entirely new approach to oilwell cementing based on the design of tailored nanocomposites. Apart from load-bearing characteristics, the cement components deployed in SAGD wellbores have to endure the severe thermal cycling inherent in the SAGD process; the oilwell cement must further be flexible and yet dense in order to avoid microannulus formation, adhere conformally to metal tubing, and provide zonal isolation[7,8,9]. HNTs have a rather similar chemical composition (Al2Si2O5(OH)4) to cement but have not been extensively explored as cement additives[17,18,19] Their porous tubular nature and deformability are promising for structural applications that require low thermal conductivity and high elastic modulus An unprecedented decrease of thermal conductivity is engineered without deleterious modification of mechanical properties, suggesting an entirely new approach to oilwell cementing
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